1. Field of the Invention
The present invention relates to an apparatus for voice communications, more specifically, to such an apparatus including or included in a telephone set.
2. Description of the Background Art
Today, voice communications over an IP (Internet Protocol) network such as the Internet are widespread. An IP network does not have such a limitation that a voice signal having its bandwidth of 4 kHz or more cannot be transmitted therein as with the public switched telephone network (PSTN) An IP network therefore enables voice communications including a broadband voice signal having the bandwidth of 4 kHz or more. Thus, high-quality voice communications with broadband voice signals could be achieved by voice communications over an IP network.
Voice communication system scan generally be classified into various voice communication systems over an IP network and other ones over an existing PSTN. Those systems are connected to one another to be a combined voice communication system.
High-quality voice communications require a telephone subscriber or terminal set adapted to a voice communication system employed. However, when communicating with somebody else on a communication network with a combined voice communication system as described above, the quality of voice communications may be deteriorated due to different voice communication systems included in the combined system.
For example, an existing ordinary telephone set, not adapted to an IP network communication, has transmitter frequency characteristics that a voice signal picked up by the microphone of the telephone set is band-limited to 4 kHz or less e.g. by a narrow band-pass filter. The telephone set also has receiver frequency characteristics that a voice signal input from the network is band-limited to 4 kHz or less e.g. by a narrow band-pass filter and then emitted from an earphone on loudspeaker. Accordingly, even though the network such as an IP network could transmit a voice signal of broader bandwidth not less than 4 kHz, the quality of voice communications to be achieved would only be the same as that of the PSTN.
Besides, if IP phones adapted to an IP network communication were used but the network between the IP phones were the PSTN or an IP network transmitting only a narrowband voice signal, a broadband voice signal (of bandwidth not less than 4 kHz) picked up by the microphone of the IP phone should not be input to the above-mentioned band-limited network, because the quality of voice communications might be deteriorated even if inputting such a broadband voice signal to the network.
For this reason, there is an increasing demand for an apparatus for voice communications that would achieve high-quality voice communications even in a combined system including different telephone sets and different networks, by taking account of different frequency bandwidths of voice signals to be transmitted between such telephone sets and networks.
It is an object of the present invention to provide a voice communication apparatus for high-quality voice communications even in the condition that voice signals of different frequency bandwidths are transmitted between different telephone sets and different networks.